Detergents are chemical agents useful for cleaning and found in many household items such as laundry and dish detergents. Detergents are usually provided as either a dry powder or as a liquid. Although some detergent components, such as surfactants, tend to be present in both dry and liquid detergents, many components are different and the manufacturing processes to produce dry or liquid detergents tend to be different. For example, dry detergents are often formed by a process called agglomeration. In agglomeration, dry materials are bound together by a binder and then dispersed in particles of a desired size, density, or other properties. Thus dry detergents may benefit from ingredients that facilitate the agglomeration process. Alternatively, dry detergents may also be produced by a spray-drying process in which the ingredients are first mixed in a liquid form. Accordingly, dry detergents may also benefit from ingredients that are soluble and that otherwise facilitate the spray-drying process.
Another problem sometimes encountered by dry detergents is caking. Caking generally refers to the tendency of dry detergent granules to stick together and thus form a solid cake, instead of remaining independent granules. Caking can interfere with dry detergent production and use. For example, it may make it difficult for consumers to remove the detergent from its container for use. Accordingly, detergent ingredients that help prevent caking are desirable.
The ability of a dry detergent or other dry material to use water or other liquids as a structural component is often referred to as its carrying capacity. Carrying capacity also reflects the ability of the dry detergent or other dry material to carry high amounts of water or other liquids and still behave as a solid powder. Detergents having a higher carrying capacity may have lower amounts of other ingredients because they are replaced by the structural water and, as a result, these detergents may have a lower cost as well as other beneficial properties. Many currently available detergents do not have a high carrying capacity and at a liquid content (typically water and liquid surfactants) above 5% may experience decreases in quality. For example, carrying capacity and caking in detergents may be related because as the liquid content of a detergent exceeds the carrying capacity, the excess liquid not used in any structural manner may cause the granules of the detergent to stick together. Many detergents develop unacceptable levels of caking for this reason at liquid content above 5%. Further, at liquid contents above 5% many detergents that contain enzymes or bleaches (particularly percarbonates or perborates), undergo decomposition of those enzymes or bleaches due the availability of non-structural water or other liquids.
Soda ash (sodium carbonate) is sometimes used to increase the carrying capacity of detergents, among other functions. Soda ash may be light or ground to increase its surface area and thus its carrying capacity. The carrying capacity of ground soda ash is approximately 25-50% of its weight. The carrying capacity of unground soda ash is approximately 15-25% of its weight. Other materials used in detergents, such as sodium sulphate used in agglomeration, typically have a carrying capacity of approximately 10-20% of their weight.
Precipitated silica (SiO2) may be used in detergents. Particles of the silica may improve detergent properties by helping with carrying capacity and agglomeration and by decreasing caking. Current silicas used in detergents are typically washed to remove various by-products of their production, such as alkali metal salts. Most alkali metal salts are removed, but for some uses, such as in battery technology, a salt content of 5-10%, particularly of sodium sulphate, may be allowed to remain. Products made with silicas may also not be as dense as is desirable, requiring additional packaging and space to transport and store the product. Accordingly, improved compositions containing silicas, particularly those useful in detergents, would be beneficial. Detergents having improvements in various properties described above are also desirable.
Silica-based compositions may also be used for a wide variety of other purposes. Accordingly, there is a need for different silica-based compositions that may serve these other purposes as well or better than current silica-based compositions. Commercially available synthetic silicas are typically derived by either a liquid phase or a vapor process. Silicas obtained by the vapor process are called fumed or pyrogenic silicas. Products obtained by liquid processes are categorized as silica gels or precipitated silicas.
Pyrogenic or fumed silicas are prepared by reacting silicon tetrachloride vapor with oxygen and hydrogen gas at high temperatures. These products have high external surface areas and differ from liquid phase-process silicas.
Silica gels are of two general types, hydrogels and aerogels. Hydrogels are typically prepared by reacting a soluble silicate such as sodium silicate with strong sulfuric acid. The gel is washed salt-free, dried, steam micronized, then classified. Aerogels are prepared from crude hydrogels by displacing the water content with an alcohol. The alcohol is then recovered by heating the gel.
Aerogels are lighter and fluffier than hydrogels because shrinkage of the gel structure is avoided during the drying process. Both types of gels tend to have very large surface areas, generally in the range of 300-1,000 m2/g and also have high porosities.
Precipitated silicas are generally formed using the process shown in FIG. 2, wherein a metal silicate and acid source are combined until silica precipitates. This silica is then washed to remove alkali metal salts and dried.
Precipitated silicas are often used as reinforcing fillers for styrene-butadiene rubber and other organic rubbers. They may also be used as fillers and extenders in toothpaste, as carrier for vitamins, as paper extenders and brighteners, and in other areas.
Accordingly, given the wide range of uses for precipitate silicas, new precipitated silica-based compositions may possibly be better suited for various uses.